The cell surface is now recognized as the primary site for the control of cell growth and development. Growth of neurites in certain cultures is greatly enhanced by the presence of nerve growth factor (NGF) in the medium. The initial action of NGF is exerted upon the NGF receptors on the axonal surface. Based on our preliminary finding of electric field effect on sensory neurite growth, we hypothesize that a direct link exists between the topological distribution of NGF-receptor complexes along the axon and the control of neurite growth. We propose to use our newly developed technique of in situ electrophoresis and NGF gradient experiments to test this hypothesis.